A method is given to obtain a good estimate of the input neutron spectrum from a pulse-height distribution measured with proportional counters filled with a hydrogenous gas. The method consists of expanding the sought estimate as a product of two functions where one is obtained by differentiating the pulse-height distribution and the other is a power series of the neutron energy. The coefficients of this series are determined by a least-squares fit of the calculated pulse-height distribution to the measured one.nThe method has been tested on pulse-height distributions obtain¬ed by calculations from a realistic neutron spectrum and response functions for a spherical counter 3. 94 cm in diameter and filled with 7 atm. of methane and 1atm of hydrogen, respectively.
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